Dc-dc converter

ABSTRACT

A DC/DC converter includes n converters connected in parallel to each other and configured to adjust a level of an input voltage according to a duty ratio of a first pulse signal applied to a first switch device to output an output voltage, wherein the n is an integer of 2 or more; and a control unit configured to compare an average of n sensing currents with the n sensing currents sensed from the converters, respectively, to adjust the duty ratio of the first pulse signal.

BACKGROUND

1. Field of the Invention

The embodiment relates to a DC/DC converter.

2. Background Art

There is a need to boost a voltage from a low voltage to a high voltageor drop a voltage from a high voltage to a low voltage in a field ofusing power.

To this end, the study of modeling and analyzing a DC-DC converter asone among various voltage boosting and dropping converters has beenperformed.

The DC/DC converters may be classified into an insulation type and anon-insulation type.

The input and output of the insulation type converter may be insulatedby using a transformer having a magnetic core, so that stability issecured. The voltage boosting and dropping ratios of the insulation typeconverter may be adjusted by adjusting a turn ratio.

The buck type converter, which is classified as one type of the DC-DCconverter, includes a forward converter, a half bridge converter and afull bridge converter. The buck-boost type converter includes a flybackconverter.

Specifically, since the flyback converter is operated even with only oneswitching device, the flyback converter may be implemented at a lowcost.

In addition, when the DC-DC converter is driven, a negative feedbackcontrol unit is used to sense and control the error of an output signalof the DC-DC converter. The DC-DC converter and the negative feedbackcontrol unit may be implemented on a single chip which may be called aswitch mode power supply unit.

Recently, in order to design a high-current DC-DC converter, a pluralityof DC-DC converters is connected to each other so that the high-currentDC-DC converter is implemented. However, when the high-current DC-DCconverter is controlled, current is concentrated into one converter dueto component deviation between the converters.

SUMMARY

The embodiment provides a DC-DC converter which is capable of processinga high current.

The embodiment provides a control unit for controlling a DC-DC convertercapable of processing a high current.

The embodiment provides a control unit for controlling a DC-DCconverter, which is capable of processing a high current, in a currentmode control scheme using a triangular wave.

The embodiment provides a control unit for controlling balance betweenthe output currents of each DC-DC converter while driving a plurality ofDC-DC converters in parallel.

According to one embodiment, there is provided a DC/DC converter whichincludes: n converters connected in parallel to each other andconfigured to adjust a level of an input voltage according to a dutyratio of a first pulse signal applied to a first switch device to outputan output voltage, wherein the n is an integer of 2 or more; and acontrol unit configured to compare an average of n sensing currents withthe n sensing currents sensed from the converters, respectively, toadjust the duty ratio of the first pulse signal.

The control unit includes: a current sensing unit configured to detectand amplify the n sensing currents to output n first output voltages; anaverage unit configured to average the n first output voltages to outputan average voltage; a current balance unit configured to compare theaverage voltage with the n first output voltages to output n secondoutput voltages; and a triangular wave generating unit configured togenerate n triangular waves having gradients adjusted according to eachof the n second output voltages.

The current sensing unit includes first to n-th current sensingsub-units, and each of the first to n-th current sensing sub-unitsdetects one of the n sensing currents and outputs one of the n firstoutput voltages.

The current balance unit includes first to n-th current balancesub-units, and each of the first to n-th current balance sub-unitscompares the average voltage with one of the n first output voltages tooutput one of the n second output voltages.

The triangular wave generating unit includes first to n-th triangularwave generating sub-units, and each of the first to n-th triangular wavegenerating sub-units outputs one of the n triangular waves which has agradient according to a level of one of the n second output voltages.

The control unit further includes: an error amplifier configured tocompare each of the n output voltages of the n converters with areference voltage and to amplify errors of the n output voltages tooutput the n control signals; and a comparator configured to compare oneof the n control signals with one of the n triangular waves to controlone of first switches of each of the n converters.

The control unit further includes n constant current sources configuredto provide mutually different currents according to each of the n secondoutput voltages.

The triangular wave generating unit includes: n capacitors charged witheach of n constant currents output from each of the n constant currentsources; n second switch devices configured to control a charge or adischarge of each of the n capacitors; and a triangular wave controlunit configured to control the n second switch devices to be turned onor off.

The triangular wave control unit controls one of the n second switchdevices based on one of charged voltages of the n capacitors and one ofthe n control signals.

The triangular wave is a voltage between both terminals of thecapacitor.

According to another embodiment, there is provided a DC/DC converterwhich includes: a plurality of converters connected in parallel to eachother and configured to adjust a level of an input voltage according toa duty ratio of a first pulse signal applied to a first switch device tooutput an output voltage; current sensing units configured to amplifysensing voltages by output currents of the converters flowing through asensing resistor in order to output first output voltages; and currentbalance units configured to amplify a differential signal between anaverage voltage of the first output voltages and one of the first outputvoltages in order to output second output voltages, wherein the dutyratio of the first pulse signal is controlled according to levels of thesecond output voltages.

Each of the current sensing units includes: a first amplifier configuredto non-inverting amplify the sensing voltage; and a second amplifierconfigured to amplify a differential signal between an output of thefirst amplifier and the sensing signal.

Each of the current balance units includes a third amplifier configuredto amplify a differential signal between an output voltage of the secondamplifier and the average voltage.

The DC/DC converter further includes a constant current sourceconfigured to output a constant current based on an output voltage ofthe third amplifier.

The DC/DC converter further includes a triangular wave generating unitconfigured to generate a triangular wave by the current output from theconstant current source.

The duty ratio of the first pulse signal is controlled according to agradient of the triangular wave output from the triangular wavegenerating unit.

The triangular wave generating unit includes: a capacitor charged withthe current output from the constant current source; a second switchdevice connected to the capacitor and configured to connect thecapacitor to a ground to discharge the capacitor; and a triangular wavecontrol unit configured to control the switch device.

The triangular wave control unit is configured to turn on or off thesecond switch device according to the charged voltage of the capacitor.

The DC/DC converter further includes an averaging unit configured togenerate the average voltage, and wherein the average unit includes abuffer configured to average the first output voltages to output theaverage voltage.

According to still another embodiment, there is provided a power supplyof an energy storage system including a DC-DC converter, which includes:n converters connected in parallel to each other and configured toadjust a level of an input voltage according to a duty ratio of a firstpulse signal applied to a first switch device to output an outputvoltage, wherein the n is an integer of 2 or more; and a control unitconfigured to compare an average of n sensing currents with the nsensing currents, respectively to adjust the duty ratio of the firstpulse signal, wherein the n sensing currents are sensed from each of theconverters.

The embodiment provides a DC-DC converter which is capable of processinga high current, and a control unit for controlling a DC-DC converter. Inaddition, the embodiment provides a control unit for controlling a DC-DCconverter, which is capable of processing a high current, in a currentmode control scheme using a triangular wave. The embodiment provides acontrol unit for controlling balance between the output currents of eachDC-DC converter while driving a plurality of DC-DC converters inparallel, so that the consumed power may be reduced when the outputcurrents of the DC-DC converters are sensed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a DC/DC converter according to anembodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a voltage mode control schemeof a DC-DC converter, and FIG. 3 is a waveform diagram illustrating adriving waveform of a control signal of FIG. 2.

FIG. 4 is a circuit diagram illustrating a current mode control schemeof a DC-DC converter, and FIG. 5 is a waveform diagram illustrating adriving waveform of a control signal of FIG. 4.

FIG. 6 is a block diagram illustrating a scheme of driving a pluralityof DC-DC converters each including a phase modulation unit, and FIG. 7is a waveform diagram illustrating sensing currents sensed by each blockof FIG. 6.

FIG. 8 is a circuit diagram showing a DC-DC converter and a control unitfor controlling the same according to the first embodiment.

FIG. 9 is a circuit diagram showing a triangular wave generating unitaccording to the first embodiment, and FIG. 10 is a waveform diagramshowing a driving waveform of the triangular wave generating unitaccording to the first embodiment,

FIG. 11 is a circuit diagram showing a constant current sourceconstituting a triangular wave generating unit according to the firstembodiment.

FIGS. 12 to 14 are views illustrating a driving waveform when theembodiment is controlled in a current discontinuous mode.

FIG. 15 is a waveform diagram showing a waveforme of the inductorcurrent iL in a current discontinuous mode.

FIGS. 16 and 17 are views illustrating problems caused in the currentcontinuous mode.

FIG. 18 is a block diagram showing a current balance control unit of aDC-DC converter according to the second embodiment.

FIG. 19 is a block diagram showing a current balance control unit incase that the DC-DC converter is driven in parallel according to thesecond embodiment.

FIG. 20 is a circuit diagram showing a current balance control unit ofthe DC-DC converter according to the second embodiment.

FIG. 21 is a circuit diagram showing a current balance control unit ofthe DC-DC converter including a triangular wave control unit accordingto the second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a multiple output converter according to an embodiment willbe described with reference to accompanying drawings. Althoughembodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. The thickness and size of an apparatus shown in thedrawings may be exaggerated for the purpose of convenience or clarity.The same reference numerals denote the same elements throughout thespecification.

FIG. 1 is a circuit diagram showing a DC-DC converter according to anembodiment.

An embodiment may include a plurality of DC-DC converters 100.

The DC-DC converter 100 may change a level of an input power Vi based ona control signal to provide an output voltage Vo to an output terminal.The plurality of DC-DC converts 100 may be connected in parallel to eachother between an input terminal of the input power Vi and the outputterminal of the output power Vo and may be driven in parallel. A singleinput power Vi may be branched to be input to the plurality of DC-DCconverters 100, and the voltages Vo output from each of the DC-DCconverters 100 may be output to a single output terminal. That is, theDC-DC converters 100 may individually process the input power Vi tooutput a single output voltage Vo.

When a single DC-DC converter is used to design a high-current DC-DCconverter, the sizes of devices in the single DC-DC converter and thecomplexity may be increased. However, according to the embodiment, theplurality of DC-DC converters 100 are connected in parallel to eachother so that the values of currents processed by each of the DC-DCconverters 100 may be reduced. Thus, a high output of power may beobtained while preventing the sizes of the devices in the DC-DCconverters 100 from being excessively increased without causing thecircuit complexity.

The DC-DC converter 100 may obtain a desired level of output power Vofrom raw input power Vi through a predetermined process. To this end, acontrol is required to obtain the desired output power Vo. Specifically,even in case that the input voltage Vi and the load current are changed,a control is required to obtain a well-adjusted output voltage Vo.

A scheme of controlling the DC-DC converter 100 is classified into avoltage mode control scheme and a current mode control scheme.

<Voltage Mode Control Scheme>

FIG. 2 is a circuit diagram illustrating a voltage mode control schemeof a DC-DC converter, and FIG. 3 is a waveform diagram illustrating adriving waveform of a control signal of FIG. 2.

First, a voltage mode control scheme will be examined with reference toFIGS. 2 and 3. As one example, a buck type DC-DC converter 100 will bedescribed.

In the buck type converter, the output voltage Vo is lower than theinput voltage Vi.

The voltage mode control type DC-DC converter 100 may include an L-C(inductor-capacitor) filter including a diode D, an inductor L and acapacitor C, a load resistor R and a switch device SW.

The switch device SW may include a transistor controlled by a controlunit 200, where one terminal of the switch device SW is connected to oneterminal of an input power source Vi and another terminal is connectedto the cathode of the diode D. One terminal of the inductor L may beconnected to the cathode of the diode, and the other terminal may beconnected to one terminal of the capacitor. The other terminal of thecapacitor may be connected to the anode of the diode and the otherterminal of the input power source Vi. The load resistor R may beconnected in parallel to the capacitor C.

The output voltage of the DC-DC converter 100 is fed back to the controlunit 200 according to the voltage mode control scheme, so that thecontrol unit 200 may generate a PWM (Pulse Width Modulation) signal forcontrolling the switch device SW of the DC-DC converter 100.

The control unit 200 may include an error amplifier 210, a comparator220 and a switch driving unit 230.

The error amplifier 210 amplifies an error of the output voltage Vo ofthe DC-DC converter 100 based on a divided voltage obtained byvoltage-dividing the output voltage Vo through first and secondresistors R1 and R2 in order to output a control voltage Vc.

The error amplifier 210 may include a first operational amplifier OP1,where the output voltage Vo of the DC-DC converter 100 is applied to theinverting terminal of the first operational amplifier OP1 through thefirst and second resistors R1 and R2 and a reference voltage Vref isapplied to the non-inverting terminal of the first operational amplifierOP1.

The error amplifier 210 compares the output voltage Vo, which isprovided through the first and second resistors R1 and R2 from the DC-DCconverter 100, with the reference voltage Vref to output an error as thecomparison result and amplifies the error. Then, the amplified error isinput to the comparator 220.

The comparator 220 generates a square wave pulse (PWM) as shown in FIG.3 based on the control voltage Vc from the error amplifier 210.

The comparator 220 may be implemented with a second operationalamplifier OP2, where the control voltage Vc from the error amplifier 210is applied to the non-inverting terminal of the second operationalamplifier OP2 and a ramp signal is applied to the inverting terminal ofthe second operational amplifier OP2.

The comparator 220 may compare the ramp signal and the control voltageVc from the error amplifier 210 with each other to generate the squarewave pulse for driving the DC-DC converter 100. Thus, the control unit200 controls the pulse width corresponding to the output error of theDC-DC converter 100, so that the output voltage Vo of the DC-DCconverter 100 may be stabilized.

The switch driving unit 230 may drive the DC-DC converter 100 based onthe square wave pulse which is an output signal of the comparator 220.That is, the switch-on and -off of the switch device included in theDC-DC converter 100 is controlled, so that the preset voltage (desiredoutput voltage Vo) of the DC-DC converter 100 may be constantlymaintained.

Referring to FIG. 3, a relationship between the duty radio of the PWMsignal and the control voltage Vc and the ramp signal may be understood.When the level of the ramp signal is equal to or less than that of thecontrol voltage Vc, a high PWM signal is output. When the level of theramp signal is higher than that of the control voltage Vc, a low PWMsignal is output. In this case, when a frequency of the ramp signal iscontrolled, the on-time and off-time of the PWM signal may be varied.Thus, the switching frequency of the DC-DC converter 100 may bedetermined by controlling the frequency of the ramp signal.

<Current Mode Control Scheme>

FIG. 4 is a circuit diagram illustrating a current mode control schemeof a DC-DC converter, and FIG. 5 is a waveform diagram illustrating adriving waveform of a control signal of FIG. 4.

The current mode control scheme is a control method of switching on aswitch with a clock of a predetermined frequency and switching off theswitch when switching current or inductor current reaches a set value.

Referring to FIGS. 4 and 5, a current mode control type DC-DC converter100 may include an L-C (inductor-capacitor) filter including a diode D,an inductor L and a capacitor C, a load resistor R and a switch deviceSW.

The output voltage of the DC-DC converter 100 is fed back to the controlunit 200 according to the current mode control scheme, so that thecontrol unit 200 may generate a PWM (Pulse Width Modulation) signal forcontrolling the switch device SW of the DC-DC converter 100.

The control unit 200 may include an error amplifier 210, a comparator220 and an RS latch.

When the operation is examined, the RS latch is set by aconstant-frequency clock. When the switch is turned on through the set,the switch current isw starts to increase. Meanwhile, the comparator 220compares a peak value of the switch current isw with an output is of theerror amplifier 210. Thus, when the switch current isw reaches to a setvalue, the RS latch is reset so that the Q is blocked. Thus, the dutyratio D is determined and the above-described operation is repeated, sothat a constant output voltage Vo having a desired level may beobtained. The switch current isw may be one of the currents flowingthrough the switch device SW, the inductor L, the diode D and the outputresistor R.

Meanwhile, in the current mode control scheme, when the duty ratio isequal to or more than 50%, a slope compensation may be additionallyperformed to prevent harmonics from occurring.

<Scheme of Driving Plural DC-DC Converters Including Phase ModulationUnit>

FIG. 6 is a block diagram illustrating a scheme of driving a pluralityof DC-DC converters each including a phase modulation unit, and FIG. 7is a waveform diagram illustrating sensing currents sensed by each block(each of the plurality of DC-DC converters) of FIG. 6.

In the drawing, the blocks A, B, C and D may represent four DC-DCconverters, respectively.

A method of driving the plurality of DC-DC converters 100 according tothe above-described current mode control scheme will be described withreference to FIG. 6.

A single output voltage Vo of the DC-DC converters 100 may be applied tothe phase modulation units 300. The output voltage Vo, which is theoutput voltage Vo of the DC-DC converter 100, may be a divided voltageVd by the voltage divider of the control unit 200.

The phase modulation units 300 may output the output having a phasedifference of 90 degrees through a phase shift.

The sensing current of the DC-DC converters 100 may be individuallysensed in the unit of blocks A, B, C and D and the sensing current maybe phase-shifted in the unit of the blocks A, B, C and D to reduceripples. Thus, when the outputs having mutually different phases aresuperimposed on each other to be complementary to each other, the ripplemay be reduced as compared with a single DC-DC converter, so that theelectromagnetic wave property may be improved.

Meanwhile, four DC-DC converters 100 and corresponding four phasemodulation units 300 are depicted in the drawings, but the embodiment isnot limited thereto and may include three phase modulation units 100 andthree phase modulation units 300. In this case, the phase modulationunits 300 may have the functions of performing phase shifts of 0, 120and 240 degrees, respectively.

<Current Mode Control Type DC-DC Converter Using Triangular Wave>

FIG. 8 is a circuit diagram showing a DC-DC converter and a control unitfor controlling the same according to the first embodiment.

A method of controlling a current mode control type DC-DC converter 100by using a triangular wave according to the first embodiment withreference to FIG. 8.

The DC-DC converter 100 according to the first embodiment may include aplurality of DC-DC converters 100 driven in parallel in order to obtaina high power, and one of the DC-DC converters 100 is depicted in FIG. 8.

The first embodiment may include a DC-DC converter 100, a control unit200 and a triangular wave generating unit 400.

The control unit 200 may include an error amplifier 210, a comparator220 and an RS latch.

Examining the operations, the RS latch is set by a constant-frequencyclock. A pulse signal may be generated in synchronization with the set.

The comparator 220 compares a peak value of the triangular wave with anoutput ic of the error amplifier 210. Thus, when the triangular wavereaches to a set value ic, the RS latch is reset so that the Q isblocked. Thus, the duty ratio D is determined and the above-describedoperation is repeated, so that a constant output voltage Vo having adesired level may be obtained.

The first embodiment is a scheme of using a sensing signal and thetriangular wave which is equivalent to the sensing current andartificially applied from the external triangular wave generating unit400. That is, the first embodiment is a scheme of using a triangularwave in the current mode control scheme.

The scheme of using a triangular wave according to such new concept mayhave the following effects.

In the current mode control scheme, the voltage of 1V is required tosense a current and if the current is sensed on the inflowing path of62.5 A, a sensing resistor of 16 mohm is required according to Ohm'slaw. In this case, the power lost at the sensing resistor is expressedas P=I_(sensing)×V_(sensing)=62.5 [W]. Thus, the very great power isconsumed by the sensing resistor. However, according to the firstembodiment, since the DC-DC converter 100 is controlled by using theequivalent triangular wave without sensing a current, the power loss maybe reduced.

<Triangular Wave Generating Unit According to the First Embodiment>

FIG. 9 is a circuit diagram showing a triangular wave generating unitaccording to the first embodiment, and FIG. 10 is a waveform diagramshowing a driving waveform of the triangular wave generating unitaccording to the first embodiment.

The triangular wave generating unit will be described with reference toFIGS. 9 and 10.

The triangular wave generating unit 400 may include a constant currentsource 410, a triangular wave control unit 420 for outputting a pulsesignal, an inverter 430 for inverting the pulse signal to output theinverted pulse signal, a first capacitor CI charged with a current ofthe constant current source 410, and a first switch device SW1controlled according to the pulse signal to control the charging ordischarging of the first capacitor C1.

When the voltage between both terminals of the first capacitor C1reaches to a level of a control signal output from the error amplifier210, the level of the pulse signal is transited from a high level to alow level. Thus, the first switch device SW1 is turned on by the pulsesignal having a low level, so that the first capacitor C1 may bedischarged.

Examining the operation relationship in detail, when a constant current(icapacitor) flows into the first capacitor C1, the voltage between bothterminals of the first capacitor C1 may be increased at a constantgradient. In detail, the relationship between voltage and current for acapacitor is expressed as

$i_{capacitor} = {C_{1}{\frac{e_{out}}{t}.}}$

Thus, the voltageboth terminals of the capacitor is expressed as

$v_{out} = {\frac{1}{C_{1}}{\int{i_{capacitor}{{t}.}}}}$

the current icapacitor of the constant current source 410 has a constantvalue K, the voltage at both terminals of the capacitor may be expressedas v_(out)=Kt[V], so that the triangular wave may be obtained.

The triangular wave control unit 420 reads out the charged voltagebetween both terminals of the capacitor from the CS terminal andcompares the charged voltage Vout with the level of a control signalbased on the control current Ic output from the error amplifier 210,such that the triangular wave control unit 420 outputs a signal Ton of ahigh level until the peak value of the charged voltage Vout reaches tothe control current Ic. The first switch may be maintained in an offstate by the inverter 430 which outputs an inverted signal of the signalTon of the high level. In addition, when the peak value of the chargedvoltage Vout reaches to the control current Ic, the signal Ton having alow level is output so that the invert 430 outputs the inverted signalhaving a high level to turn on the first switch device SW1, so that thefirst capacitor C1 may be discharged. In addition, the triangular wavegenerating unit 420 may read out a clock signal in order to synchronizethe set of the RS latch of the control unit 200.

While the above-described operation is repeated, the triangular wavegenerating unit 400 may generate the triangular wave.

A duty ratio (time periode ratio), which is a ratio between the on timeand off time of the switch SW included in the DC-DC converter 100, maybe varied by the triangular wave. When the duty ratio is varied, thedegree of controlling a level of the input power Vi of the DC-DCconverter 100 may be varied.

Meanwhile, when the DC-DC converter 100 includes a plurality of DC DCconverters connected in parallel to each other, the control unit 200 mayinclude a plurality of control units 200 for controlling the DC-DCconverters 100, respectively.

In addition, the DC-DC converter 100 may be called a converter, or theconverter and the control unit 200 may constitute the DC-DC converter100.

<Constant Current Source of Triangular Wave Generating Unit>

FIG. 11 is a circuit diagram showing a constant current sourceconstituting a triangular wave generating unit according to the firstembodiment.

Referring to FIG. 11, the constant current source 410 of the triangularwave generating unit 400 is illustrated in detail.

In the constant current source 410, a reference voltage Vref is dividedby resistors R3 and R4 and the divided voltage is input to thenon-inverting terminal (+) of a third operational amplifier OP3. Asecond switch SW2 is turned on by a voltage difference between thereference voltage Vref and a divided voltage Vd (which is different fromthe divided voltage Vd of FIG. 4) of both terminals of a resistor R5while the divided voltage Vd is input to the inverting terminal (−) ofthe third operational amplifier OP3. And, as the second switch SW2 isturned on, the first capacitor C1 may be charged with a constant currentIcapacitor.

As the first capacitor C1 is charged, the voltage Vout is increased. Thetriangular wave control unit 420 reads out the increasing voltage Voutand outputs the signal Ton having a low level when the voltage Voutreaches to the value of the control current Ic. Thus, the first switchSW1 is turned on so that the first capacitor C1 is discharged. While theabove-described operation is repeated, the triangular wave may be outputto the terminal Vout.

FIGS. 12 to 15 are views illustrating driving a waveform when theembodiment is controlled in a current discontinuous mode.

When the first embodiment is operated in the current discontinuous mode,the effect may be maximized.

Referring to FIGS. 12 to 14, in the DC-DC converter 100, a time periodthat the current flowing through the inductor L becomes 0 (zero) mayoccur according to the load resistor R or the inductance of the inductorL. During the time period, the switch device SW and the diode D all maybe turned off. The operation mode, in which there may exist a state thatthe inductor current is 0 (zero), is called a current discontinuousmode.

Hereinafter, the condition for allowing the current of the inductorcurrent to be operated in the discontinuous mode will be described.

Before describing the condition for an operation in the discontinuousmode, a steady state for the inductor current iL and the output voltageVo will be analyzed.

<Steady State Analysis>

<Steady State Analysis-Current Increasing Section 0≦t<DT>

When the switch device SW is switched at a period T and a duty ratio D,the current iL and voltage vL of the inductor L are depicted in FIG. 13.

During a section DT for a switching period T, when KVL (Kirchhoff'sVoltage Law) is applied to the DC-DC converter 100, the inductor voltagevL may be obtained through the following equation 1:

v _(L) =V _(i) −v _(o)   (1)

In addition, the relationship between the current iL and the voltage vLof the inductor L may be expressed as the following equation 2:

$\begin{matrix}{v_{L} = {L\frac{i_{L}}{t}}} & (2)\end{matrix}$

From the equations 1 and 2, the gradient of the current flowing throughthe inductor may be expressed as the following equation 3:

$\begin{matrix}{\frac{i_{L}}{t} = \frac{V_{i} - v_{o}}{L}} & (3)\end{matrix}$

However, in the steady state, since the output voltage vo is less thanthe input voltage vi, during the section DT for which the switch deviceSW is connected to the input power source, the inductor current iL isincreased at the gradient of the equation 3. As shown in FIG. 13, theinductor current is the minimum current Imin at the moment that theswitch device SW is connected to the power source (t=0). After the timeDT is elapsed from the time at which the switch device SW is connectedto the power source (t=DT), the inductor current is increased to themaximum current Imax. Thus, the equation 3 may be expressed as thefollowing equation 4:

$\begin{matrix}{{i_{L}(t)} = {{\frac{1}{L}{\int_{0}^{t}{\left( {V_{i} - v_{o}} \right)\ {t}}}} + I_{\min}}} & (4)\end{matrix}$

From the equation 4, the maximum current Imax of the inductor may beexpressed as the following equation 5:

$\begin{matrix}{{i_{L}({DT})} = {I_{\max} = {{\frac{1}{L}{\int_{0}^{DT}\ {\left( {V_{i} - v_{o}} \right){t}}}} + I_{\min}}}} & (5)\end{matrix}$

Here, when a ripple component of the output voltage vo is mostly removedby the L-C filter of the inductor L and the capacitor C, the outputvoltage vo may be a constant DC voltage. In this case, if the integralexpression of equation 5 is analyzed, the current iL of the inductor Lis increased during the DT section as the following equation 6:

$\begin{matrix}{{I_{\max} - I_{\min}} = {\frac{V_{i} - V_{o}}{L} \times {DT}}} & (6)\end{matrix}$

<Steady State Analysis-Current Decreasing Section DT≦t<T>

While the switch SW is turned off during the (1-D)T section, the DC-DCconverter 100 is operated as shown in FIG. 14.

When KVL (Kirchhoff's Voltage Law) is applied to the circuit, theinductor voltage vL may be obtained through the following equation 7:

v _(L) =−v _(o)   (7)

Since the relationship between the inductor current iL and the inductorvoltage vL is equal to the equation 2, the gradient of the inductorcurrent iL is expressed as the following equation 8:

$\begin{matrix}{\frac{i_{L}}{t} = {- \frac{v_{o}}{L}}} & (8)\end{matrix}$

However, in the steady state, the output voltage vo is greater than 0(zero). During the section (1-D)T from the moment when the switch deviceSW is turned of, the inductor current iL is decreased at the gradientlike the graph depicted in FIG. 13. That is, the inductor current iL isincreased to the maximum current Imax at the moment (t=DT) when theswitch device SW is turned off. After the time of (1-D)T is elapsed, theinductor current iL is decreased to the minimum current Imin at t=T.From the equation 8, the inductor current iL is expressed as thefollowing equation 9:

$\begin{matrix}{{i_{L}(t)} = {{\frac{1}{L}{\int_{DT}^{t}\ {\left( {- v_{o}} \right){t}}}} + I_{\max}}} & (9)\end{matrix}$

The minimum value Imin of the inductor current is expressed as thefollowing equation 10:

$\begin{matrix}{{i_{L}\left( {t = T} \right)} = {I_{\min} = {{\frac{1}{L}{\int_{DT}^{T}{\left( {- v_{o}} \right)\ {t}}}} + I_{\max}}}} & (10)\end{matrix}$

Here, it is assumed that the AC components are mostly removed by the L-Cfilter, the output voltage vo becomes a constant DC voltage. In thiscase, if the integral expression of equation 10 is analyzed, theinductor current iL is varied during the DT section as the followingequation 11:

$\begin{matrix}{{I_{\min} - I_{\max}} = {{- \frac{V_{o}}{L}} \times \left( {1 - D} \right)T}} & (11)\end{matrix}$

<Steady State Analysis-Output Voltage Vo>

As shown in FIG. 13, the inductor current iL is increased during the DTsection and decreased during the (1-D)T section. In the steady state,since the current increasing amplitude is equal to the currentdecreasing amplitude, from the equations 6 and 11, the average value Voof the output voltages may be expressed as the following equation 12.

$\begin{matrix}{{\frac{V_{i} - V_{o}}{L} \times {DT}} = {{- \frac{V_{o}}{L}} \times \left( {1 - D} \right)T}} & (12)\end{matrix}$

The equation 12 may be expressed as following equation 13:

v _(o) −DV _(i)   (13)

<Output Voltage iL>

According to the switching operation of the switch device SW of theDC-DC converter 100, the inductor current iL may be obtained byanalyzing the equations 5 and 9. However, since the increase anddecrease of the inductor current iL is linearly varied as shown in FIG.13, the average value IL of the currents flowing the-ought the inductorL is obtained from the following equation 14:

$\begin{matrix}{I_{L} = \frac{I_{\max} + I_{\min}}{2}} & (14)\end{matrix}$

In FIG. 14, when KCL is applied, the following equation 15 may beobtained:

However, when the average value of the capacitor current is Ic in thesteady state, since the average value Ic is 0 (zero), the average valueIL of the inductor current is equal to Io which is an average value ofthe inductor current iL. That is, this is expressed as the followingequation 16:

$\begin{matrix}{I_{L} = {I_{o} = \frac{V_{o}}{R}}} & (16)\end{matrix}$

Thus, from the equations 12, 14 and 16, the minimum value Imin and themaximum value Imax of the inductor current iL may be obtained as thefollowing equations 17 and 18:

$\begin{matrix}{I_{\max} = {{I_{L} + {V_{o} \times \frac{1 - D}{2L} \times T}} = {I_{o} + {V_{i} \times \frac{D\left( {1 - D} \right)}{2L} \times T}}}} & (17) \\{I_{\min} = {{I_{L} - {V_{o} \times \frac{1 - D}{2L} \times T}} = {I_{o} - {V_{i} \times \frac{D\left( {1 - D} \right)}{2L} \times T}}}} & (18)\end{matrix}$

<Current Discontinuous Mode>

FIG. 15 is a waveform diagram showing a waveforme of the inductorcurrent IL in a current discontinuous mode.

The condition for allowing the DC-DC converter 100 to be operated in thecurrent discontinuous mode as shown in FIG. 15 is that the minimum valueImin of the inductor current is less than 0 (zero). Thus, the conditionthat the minimum value Imin expressed as the equation 18 is less than 0is expressed as the following equation

$\begin{matrix}{I_{\min} = {{I_{L} - {V_{o} \times \frac{1 - D}{2L} \times T}} = {{I_{o} - {V_{i} \times \frac{D\left( {1 - D} \right)}{2L} \times T}} < 0}}} & (19)\end{matrix}$

That is, under the condition of the equation 19, the first embodimentmay be operated in the current discontinuous mode.

For example, the DC-DC converter 100 may be operated in the currentdiscontinuous mode when the input power of the DC-DC converter 100 is100V, the switch device SW is controlled at a switching frequency of 100kHz, the capacitance of the capacitor C is sufficiently great such thatthe output voltage vo is constant, the inductance of the inductor L is50 uH, the duty ratio is 0.5, and the output current Io is less than 2.5A from the equation 19.

The conditions for the operation of the current discontinuous mode havebeen described above. Hereinafter, problems caused when the firstembodiment is operated in the current continuous mode will be described.

FIGS. 16 and 17 views illustrating problems caused in the currentcontinuous mode.

Referring to FIGS. 16 and 17, due to deviations between the devices ofeach DC-DC converter 100 of the blocks A, B, C and D, the turn-on and-off times of the first switch SW1 of the triangular wave control unit420 of the triangular wave generating unit 400 may be varied. In thiscase, the gradient of the triangular wave may be varied, that is,TA>TB=TC=TD in the drawing. Thus, a phenomenon of concentrating currentinto the block A having the most gradient of the triangular wave mayoccur. Thus, although the block A enters the current continuous mode asthe output current of the block A is increased, the currents of theremaining blocks B, C and D are in the current discontinuous mode.Therefore, when the first embodiment is used not in the currentdiscontinuous mode but in the current continuous mode, each block may beoperated in a mixed mode of the current continuous and discontinuousmodes. Thus, when the DC-DC converter is maintained in the currentdiscontinuous mode according to the condition of the equation 19, thecurrent may be prevented from being concentrated into one of the blocksand all blocks may be maintained in the current discontinuous mode.Therefore, a desired output may be obtained and in addition, any sensingresistors for sensing current are not required, so that the power lossmay be reduced.

Meanwhile, the first embodiment is applicable to an energy charge systemand specifically, usable for an LED control power supply.

Among a main converter and supplementary converters constituting the LEDcontrol power supply, the embodiment may be applied to the supplementaryconverters operated in the current discontinuous mode.

In addition, since power conditioning is important in equipmentconnected to an electrical distribution network and a PFC (Power FactorCorrection) circuit may be controlled in the current discontinuous mode,the embodiment may be applied to the PFC circuit.

<Current Balance Control Unit of DC-DC Converter>

FIG. 18 is a block diagram showing a current balance control unit of aDC-DC converter according to the second embodiment.

Referring to FIG. 18, the current balance control unit 500 constitutingthe control unit 200 for controlling the DC-DC converter 100 may includea first current sensing unit 511, a first current balace unit 521 , afirst constant current unit 531, a first triangular wave generating unit541 and an average unit 550.

The first current sensing unit 511 may sense an output current of theDC-DC converter 100 to output an amplified voltage VI (A) based on thesensed output current.

The average unit 550 may average the voltage V1(A) output from the firstcurrent sensing unit 511 and the voltages output from each of the DC-DCconverters connected in parallel to each other to output the averagevalue.

The first current balance 521 may amplify the difference signal betweenthe output voltage V1(A) output from the first current sensing unit 511and the average voltage VAVG to output a second output voltage Vo(A).

The first constant current unit 531 may output a constant current basedon the second output voltage Vo(A) output from the first current balanceunit 521 and a reference voltage Vref.

The first triangular wave generating unit 541 may output a triangularwave Vout(A) having a gradient based on the current value output fromthe first constant current unit 531.

FIG. 19 is a block diagram showing a current balance control unit incase that the DC-DC converter is driven in parallel according to thesecond embodiment.

According to the second embodiment, each of the n DC-DC converters 100,which are connected in parallel to each other, include a switch device.A level of the input voltage Vi applied to the DC-DC converter 100 iscontrolled according to the duty ratio of a first pulse signal appliedto the switch device and is output as the output voltage Vo.

Each of the n control units 200 may detect the currents from the n DC-DCconverters 100 and compare an average value of the detected currentswith one of the detected currents in order to control the duty ratio ofthe first pulse signal.

The current balance control unit 500 may include a current sensing unit510 for detecting and amplifying the n sensing currents Iout(A) Iout(n)to output n first output voltages, an average unit 550 for averaging then first output voltages V1(A)˜V1(n) to output the average voltage VAVG,a current balance unit 520 for comparing the average voltage VAVG withthe n first output voltages V1(A)˜V1(n) to output n second outputvoltages Vo(A)˜Vo(n), and a triangular wave generating unit 540 forgenerating n triangular waves Vout(A)˜Vout (n) having gradients adjustedaccording to the n second output voltages Vo(A)˜Vo(n), respectively.

The current sensing unit 510 may include first to n-th current sensingsub-units 511 to 514. The first to n-th current sensing sub-units 511 to514 may detect the n sensing currents Iout(A)˜Iout(n) to output the nfirst output voltages V1(A)˜V1(n), respectively. That is, the firstcurrent sensing sub-unit 511 may detect the first sensing currentIout(A) to output the (1-1)-th output voltage V1(A), and the n-thcurrent sensing sub-unit may detect the n-th sensing current Iout(n) tooutput the (1-n)-th output voltage V1(n).

The current valance unit 520 may include first to n-th current balancesub-units 521 to 524. The first to n-th current balance sub-units 521 to524 may compare the average voltage VAVG with the n first outputvoltages V1(A)˜V1(n) to output the n second output voltages Vo(A)˜Vo(n),respectively. That is, the first current balance sub-unit 521 maycompare the average voltage VAVG with the (1-1)-th output voltage V1(A)to output the (2-1)-th output voltage Vo(A), and the n-th currentbalance sub-unit 524 may compare the average voltage VAVG with the(1-n)-th output voltage V1(n) to output the (2-n)-th output voltageVo(n).

The triangular wave generating unit 540 may include first to n-thtriangular wave generating sub-units 541 to 544. The first to n-thtriangular wave generating sub-units 541 to 544 may output the ntriangular waves Vout(A)˜Vout(n) having gradients determined based onlevels of the n second output voltages Vo(A)˜Vo(n), respectively. Thatis, the first triangular wave generating sub-unit 541 may output thefirst triangular wave Vout(A) having the gradient determined based onthe level of the (2-1)-th output voltage Vo(A), and the n-th triangularwave generating sub-unit may output the n-th triangular wave Vout(n)having the gradient determined based on the level of the (2-n)-th outputvoltage Vo(n).

The control unit 200 may include an error amplifier 210 for comparingthe n output voltages of the n DC-DC converters 100 with the referencevoltage Vref and for amplifying errors of the n output voltages tooutput the n control signals Ic, respectively, and a comparator 220 forcomparing the n control signals Ic (Icontrol) with the n triangularwaves Vout(A)˜Vout(n) to control the switch devices SW included in the nDC-DC converters 100, respectively.

The control unit 200 may further include n constant current sources 531to 534 for providing currents according to each of the n second outputvoltages Vo(A)˜Vo(n).

The triangular wave generating unit 540 may include n capacitors Ccharged with n constant currents Ic (Icapacitor) output from the nconstant current sources 531 to 534, respectively, n second switchdevices SW2 for controlling the charges or discharges of the ncapacitors C, and a triangular wave control unit 420 for controlling theturn-on or-off operations of the n second switch devices SW2.

The triangular wave control unit 420 may control the n second switchdevices SW2 based on the charged voltages of the n capacitors C and then control signals Ic (Icontrol), respectively. In addition, thetriangular wave is a voltage between both terminals of the capacitor C.

In this case, the DC-DC converter 100 may be a buck type.

The above-described operations will be examined in detail with referenceto FIG. 19. When the plurality of DC-DC converters 100 are connected inparallel to each other to be driven, the current balance control unit500 may include a plurality of current sensing units 510, a plurality ofcurrent balance units 520, a plurality of constant current units 530 anda plurality of triangular wave generating units 540.

The four DC-DC converters 100 driven in parallel are depicted in thedrawing, but the embodiment is not limited thereto. That is, theembodiment may provide more than or less than four DC-DC converters 100driven in parallel.

When the four DC-DC converter 100 are driven in parallel, the currentsensing unit 510 of the current balance control unit 500 may include thefirst to fourth current sensing sub-units 511 to 514. In addition, thecurrent balance unit 520 may include the first to fourth current balacesub-units 521 to 524 and the constant current unit 530 may include thefirst to fourth constant current sources 531 to 534. Further, thetriangular wave generating unit 540 may include the first to fourthtriangular wave generating sub-units 541 to 544.

The four DC-DC converters 100 may represent the blocks A, B, C and D,respectively.

In addition, the current balance control unit 500 according to thesecond embodiment may further include the average unit 550 whichreceives the output signals output from the first to fourth currentsensing sub-units 511 to 514 to output the average of the outputsignals.

The first to fourth current sensing sub-units 511 to 514 may detect theoutput currents Iout(A), Iout(B), Iout(C) and Iout(D) from the fourDC-DC converters 100 connected in parallel to each other, respectively.

The output currents Iout(A), Iout(B), Iout(C) and Iout(D) are currentsflowing through the inductors L, the diodes D or the output loads Rconstituting the DC-DC converters 100

The first to fourth current sensing sub-units 511 to 514 may sense theoutput currents Iout(A), Iout(B), Iout(C) and Iout(D) and amplify thesensed output currents to output the first output voltages V1(A), V1(B),V1(C) and V1(D), respectively.

The first to fourth current balance sub-unit 521 to 524 may receive thefirst output voltages V1(A), V1(B), V1(C) and V1(D), respectively. Inaddition, the average unit 550 may receive the first output voltagesV1(A), V1(B), V1(C) and V1(D).

The average unit 550 may output the average voltage VAVG based on thefirst output voltages V1(A), V1(B), V1(C) and V1(D).

The first to fourth current balance sub-unit 521 to 524 may outputdifferential second output voltages Vo(A), Vo(B), Vo(C) and Vo(D) basedon the average voltage VAVG output from the average unit 550 and thefirst output voltages V1(A), V1(B), V1(C) and V1(D), respectively.

The first to fourth constant current sources 531 to 534 may outputconstant currents based on the differential second output voltagesVo(A), Vo(B), Vo(C) and Vo(D) and the reference voltage Vref,respectively.

The first to fourth triangular wave generating sub-units 541 to 544 mayuse the constant currents output from the first to fourth constantcurrent source sub-units 531 to 534 to output the triangular wavesVout(A), Vout(B), Vout(C) and V(out(D) to the blocks A, B, C and D, thatis, the four DC-DC converters 100, respectively.

In detail, the triangular waves Vout(A), Vout(B), Vout(C) and V(out(D)may be applied to the non-inverting terminal (+) of the comparator 220in FIG. 8, respectively.

The turn-on and -off times of the switch devices SW included in theDC-DC converters 100, that is, the duty ratios may be varied with thegradients of the triangular waves Vout(A), Vout(B), Vout(C) and V(out(D)output from the first to fourth triangular wave generating sub-units 541to 544.

The gradients of the triangular waves Vout(A), Vout(B), Vout(C) andV(out(D) may vary according to the levels of the second output voltagesVo obtained by differentially amplifying the first output voltages andthe average voltage VAVG.

When the output current output from one of the blocks A, B, C and D isgreater than the average value, the second output voltage is decreasedso that the triangular wave is increased, thereby decreasing the turn-ontime.

When the turn-on time is decreased, the output current of thecorresponding block is decreased. The output currents of the blocks A,B, C and D may be balanced through the above-described scheme.

<Circuit Diagram of Current Balance Control Unit of DC-DC Converter>

FIG. 20 is a circuit diagram showing a current balance control unit ofthe DC-DC converter according to the second embodiment.

Referring to FIGS. 19 and 20, the current balance control unit 500 ofthe DC-DC converter 100 according to the second embodiment may includefirst to fifth amplifiers OP1 to OP5.

The n DC-DC converters 100, which are connected in parallel to eachother, include switch devices, respectively (where n is an integer of 2or more). The level of the input voltage applied to the DC-DC converter100 is adjusted according to the duty ratio of the first pulse signalapplied to the switch device SW and outputs, the output voltage.

In addition, the current sensing unit 510 of the DC-DC converter 100 mayamplify the sensing voltages Vout to output the first output voltagesV1, where the sensing voltages Vout are based on the output currentsIout of the DC-DC converters 100 flowing through the sensing resistorsR1 for sensing the currents of the DC-DC converts 100. The currentbalance unit 520 may amplify the differential signal between the averagevoltage VAVG of the first output voltages V1 and the first outputvoltages V1 to output the second output voltages Vo. Further, the ratioof the first pulse signal may be controlled according to the levels ofthe second output voltages Vo.

Each of the current sensing units 510 may include the first amplifierOP1 for non-inverting amplifying the sensing voltage Vout and the secondamplifier OP2 for amplifying the differential signal between the outputof the first amplifier OP1 and the sensing voltage Vout.

Each of the current balance units 520 may include the third amplifierOP3 for amplifying the differential signal between the output voltage V1of the second amplifier OP2 and the average voltage VAVG.

The configuration for controlling the DC-DC converter may furtherinclude the constant current source 430 for outputting a constantcurrent based on the output voltage of the third amplifier OP3 and thetriangular wave generating unit 540 for generating the triangular wavebased on the current Ic (Icapacitor) output from the constant currentsource 430.

The triangular wave generating unit 540 may include a capacitor Ccharged with the current Ic (Icapacitor) output from the constantcurrent source 530, a second switch device SW2 connected between thecapacitor C and the ground to discharge the capacitor C, and atriangular wave control unit 420 for controlling the second switchdevice SW2.

The triangular may allow the second switch device SW2 to be turned on oroff according to the charged voltage of the capacitor C.

As a configuration for control the DC-DC converter 100, an average unit550 may be further provided to generate the average voltage VAVG. Theaverage unit 550 may include a buffer OP5 for averaging the first outputvoltages VI.

Meanwhile, the gradient of the triangular wave may be controlled bycomparing the level of one of the sensing voltages Vout with the levelof the average voltage VAVG.

Hereinafter, the second embodiment will be described in detail withreference to FIG. 20.

Each of the first to fourth current sensing sub-units 511 to 514 mayinclude the first and second amplifiers ON and OP2 and the first toseventh resistors R1 to R7. Each of the first to fourth current balancesub-units 521 to 524 may include the third amplifier OP3 and the eighthto tenth resistors R8 to R10. Each of the first to fourth constantcurrent sources 531 to 534 may include the fourth amplifier OP4, thefirst switch SW1, and the eleventh and twelfth resistors R11 and R12.Each of the first to fourth triangular wave generating sub-units 541 to544 may include the second switch SW2 and a capacitor C. And, theaverage unit 550 may include the fifth amplifier OP5 and the 13-th to18-th resistors R14 to R18.

Hereinafter, the connections between the amplifiers ON to OP4, which maybe configured with operational amplfiers, and the resistors will bedescribed.

The first amplfier OP1 may include a non-inverting amplifier. Thenon-inverting terminal (+) of the first amplfier OP1 may be connected toa current sensing node of the block A, B, C or D. The first resistor R1may be connected between the current sensing node and a node N. The,second resistor R2 may be connected between the inverting terminal (−)of the first amplifier OP1 and the node N. And, the third resistor R3may be connected between the output terminal of the first amplifier OP1and the inverting terminal (−).

The fourth resistor R4 may be connected between the output terminal ofthe first amplifier OP1 and the inverting terminal (−).The fifthresistor R5 may be connected between the output terminal of the firstamplifier OP1 and the non-inverting terminal of the second amplifier.The sixth resistor R6 may be connected between the non-invertingterminal (+) of the second amplfier OP2 and the ground. The seventhresistor R7 may be connected between the inverting terminal (−) of thesecond amplifier OP2 and the output terminal of the second amplfier OP2.

The eighth resistor R8 may be connected between the output terminal ofthe second amplifier OP2 and the inverting terminal (−) of the thirdamplifier OP3. The ninth resistor, which is a resistor for configuring anegative feedback of the third amplfier OP3, may be connected betweenthe inverting terminal (−) of the third amplifier OP3 and the outputterminal of the third amplifier OP3.

The tenth resistor RIO may be connected between the output terminal ofthe third amplifier OP3 and the non-inverting terminal (+) of the fourthamplifier OP4. The eleventh resistor R11 may be connected between thereference voltage supply terminal Vref and the non-inverting terminal(+) of the fourth amplifier OP4. The twelfth resistor R12 may beconnected between the reference voltage supply terminal Vref and theinverting terminal (−) of the fourth amplifier OP4. The twelfth resistorR12 may be connected between the reference voltage supply terminal Vrefand the emitter of the first switch SW1. The output terminal for thefourth amplifier OP4 may be connected to the base of the first switchSW1.

The capacitor C may be connected between the emitter of the first switchSW1 and the ground, and may be connected between the drain of the secondswitch SW2 and the ground.

The second switch SW2 may be turned on or off according to the controlsignal applied to the gate of the second switch SW2. The drain of thesecond switch SW2 may be connected to the emitter of the first switchSW1 and the source may be connected to the ground.

The first switch SW1 may include a bipolar junction transistor (BJT) andthe second switch SW2 may include an MOSFET transistor, but theembodiment is not limited thereto and any devices may be used if thedevices can perform a switching function.

The 13-th resistor R13 may be connected between the output terminal ofthe second amplifier OP2 of the first current sensing sub-unit 511 andthe non-inverting terminal (+) of the fifth amplifier OP5. The 14-thresistor R14 may be connected between the output terminal of the secondamplifier OP2 of the second current sensing sub-unit 512 and thenon-inverting terminal (+) of the fifth amplifier OP5. The 15-thresistor R15 may be connected between the output terminal of the secondamplifier OP2 of the third current sensing sub-unit 513 and thenon-inverting terminal (+) of the fifth amplifier OP5. The 16-thresistor R16 may be connected between the output terminal of the secondamplifier OP2 of the fourth current sensing sub-unit 514 and thenon-inverting terminal (+) of the fifth amplifier OP5. The 17-thresistor R17 may be connected between the output terminal of the fifthamplifier OP5 and the non-inverting terminal (+) of the third amplifierOP3. The 18-th resistor R18 may be connected between the non-invertingterminal (+) of the third amplifier OP3 and the ground. The invertingterminal (−) and the output terminal of the fifth amplifier OP5 may beconnected to each other so that the fifth amplifier OP5 may be operatedas a buffer following the voltage of the non-inverting terminal (+)thereof.

<Operation Type of Current Balance Control Unit>

Hereinafter, the operation of the current balance control unit 500according to the second embodiment will be described.

For the purpose of convenient description, the following descriptionwill be focused on the first current sensing sub-unit 511, the currentbalance sub-unit 521, the first constant current source 531, the firsttriangular wave generating sub-unit 541 and the average unit 550corresponding to the block A. The same operation is applicable to theremaining blocks.

The output current (sensing current) lout(A) of the block A applied tothe first current sensing sub-unit 511 passes through the first resistorR1 to generate a voltage (sensing voltage) Vout at the node N. Thevoltage Vout of the node N may be expressed as the following equation 1:

V _(out) R ₁ ×I _(out(A))   (1)

The first resistor R1 may become a sensing resistor. Thus, when thesensing current Iout(A) is detected, the sensing voltage Vout may bedetected through the first resistor R1.

According the non-inverting amplification property of the firstamplifier OP1, the output V1 of the first amplifier OP1 may be expressedas the following equation 2:

$\begin{matrix}{V_{1} = {{\left( {1 + \frac{R_{3}}{R_{2}}} \right)V_{out}} = {\left( {1 + \frac{R_{3}}{R_{2}}} \right)I_{{out}{(A)}} \times R_{1}}}} & (2)\end{matrix}$

When KCL is applied to both input terminals of the second amplifier OP2of the first current sensing sub-unit 511, the output V1(A) may beexpressed as the following equation 3:

$\begin{matrix}{V_{1{(A)}} = {{\frac{\left( {R_{4} + R_{7}} \right)R_{8}}{R_{4}\left( {R_{5} + R_{6}} \right)}V_{1}} - {\frac{R_{7}}{R_{8}}V_{out}}}} & (3)\end{matrix}$

When the second amplifier OP2 is operated as a differential amplifier,the relationship between the resistors connected to the second amplifierOP2 may be expressed as the following equation 4:

$\begin{matrix}{\frac{R_{7}}{R_{4}} = \frac{R_{6}}{R_{5}}} & (4)\end{matrix}$

From the equation 4, the equation 3 may be written as the followingequation 5:

$\begin{matrix}{V_{I{(A)}} = {{\frac{R_{7}}{R_{4}}\left( {V_{1} - V_{out}} \right)} = {\frac{R_{7}}{R_{4}}\left( {V_{1} - {R_{1}I_{out}}} \right)}}} & (5)\end{matrix}$

According to the equation 5, when the sensing current Iout(A) isincreased, the voltage value of the first output voltage V1(A) may bedecreased.

When the voltage of the non-inverting terminal (+) of the average unit500 is denoted as V+(OP5) and KCL is applied at the non-invertingterminal (+), the following equation 6 is obtained:

$\begin{matrix}{{\frac{V_{+ {({{OP}\; 5})}} - V_{1{(A)}}}{R_{13}} + \frac{V_{+ {({{OP}\; 5})}} - V_{1{(B)}}}{R_{14}} + \frac{V_{+ {({{OP}\; 5})}} - V_{1{(C)}}}{R_{15}} + \frac{V_{+ {({{OP}\; 5})}} - V_{1{(D)}}}{R_{16}}} = 0} & (6)\end{matrix}$

The equation 6 may be rewritten as the following equation 7:

$\begin{matrix}{{\left( {\frac{1}{R_{13}} + \frac{1}{R_{14}} + \frac{1}{R_{15}} + \frac{1}{R_{16}}} \right)V_{+ {({{OP}\; 5})}}} = {\frac{V_{1{(A)}}}{R_{13}} + \frac{V_{1{(B)}}}{R_{14}} + \frac{V_{1{(C)}}}{R_{15}} + \frac{V_{1{(D)}}}{R_{16}}}} & (7)\end{matrix}$

In order to calculate the average of the output voltages V1(A), V1(B),V1(C) and V1(D) from the first to fourth current sensing sub-units 511to 514 corresponding to the blocks A, B, C and D, the relationshipbetween the resistors of the average unit 550 may be expressed as thefollowing equation 8:

$\begin{matrix}{\frac{1}{R_{13}} + \frac{1}{R_{14}} + \frac{1}{R_{15}} + \frac{1}{R_{16}}} & (8)\end{matrix}$

When the equation 8 is applied to the equation 7, the voltage V+(OP5) ofthe non-inverting terminal (+) of the fifth amplifier OP5 is expressedas the following equation 9:

$\begin{matrix}{V_{+ {({{OP}\; 5})}} = {\frac{1}{4}\left( {V_{1{(A)}} + V_{1{(B)}} + V_{1{(C)}} + V_{1{(D)}}} \right)}} & (9)\end{matrix}$

According to the characteristics of an amplifier, the following equation10 is obtained:

V _(AVG) =V _(−(OP5)) =V _(+(OP5))   (10)

From the equation 10, the average voltage VAVG of the output voltagesV1(A), V1(B), V1(C) and V1(D) from each of the first to fourth currentsensing sub-units 511 to 514 corresponding to the blocks A, B, C and Dmay be calculated.

According to the differential amplification characteristics of the thirdamplifier OP3 of the first current balance unit 521, the output voltageof the third amplifier OP3 may be expressed as the following equation11:

$\begin{matrix}{V_{o{({{OP}\; 3})}} = {{\frac{\left( {R_{8} + R_{8}} \right)R_{10}}{R_{8}\left( {R_{17} + R_{18}} \right)}V_{AVG}} - {\frac{R_{8}}{R_{8}}V_{1{(A)}}}}} & (11)\end{matrix}$

Taking into consideration the differential amplification characteristicsof the third amplifier OP3, the relationship of the resistors connectedto the third amplifier OP3 is expressed as the following equation 12:

$\begin{matrix}{\frac{R_{9}}{R_{8}} = \frac{R_{18}}{R_{17}}} & (12)\end{matrix}$

When the equation 12 is applied to the equation 11, the output voltageof the third amplifier OP3 is expressed as the following equation 13:

$\begin{matrix}{\mspace{79mu} {{V_{o{({{OP}\; 3})}} = {\frac{\text{?}}{\text{?}}\left( {V_{AVG} - V_{1{(A)}}} \right)}}{\text{?}\text{indicates text missing or illegible when filed}}}} & (13)\end{matrix}$

According to the equation 13, when the voltage of the first outputvoltage V1(A) is decreased, it is known that the voltage value of theoutput voltage Vo(OP3) of the third amplifier OP3 is decreased.

When KLC is applied to the node of the non-inverting terminal (+) of thefourth amplifier OP4 constituting the first constant current source 531,the following equation 14 is obtained:

$\begin{matrix}{{\frac{V_{o{(A)}} - V_{o{({{CP}\; 3})}}}{R_{10}\;} + \frac{V_{o{(A)}} - V_{ref}}{R_{11}}} = 0} & (14)\end{matrix}$

When the equation 14 is rewritten, the second output voltage Vo(A) isexpressed as the following equation 15:

$\begin{matrix}{V_{o{(A)}} = {\frac{R_{18} \times R_{16}}{R_{10} + R_{11}}\left( {{\frac{1}{10}V_{o{({{OP}\; 3})}}} + {\frac{1}{R_{11}}V_{ref}}} \right)}} & (15)\end{matrix}$

When the resistors of the first constant current source 531 satisfiesthe following equation 16, the second output voltage is expressed as thefollowing equation 17:

$\begin{matrix}{R_{10} = R_{11}} & (16) \\{V_{o{(A)}} = {\frac{1}{2}\left( {V_{o{({{OP}\; 5})}} + V_{ref}} \right)}} & (17)\end{matrix}$

According to the characteristics of the operational amplifier of thefourth amplifier OP4, the following equation is obtained:

V _(B) =V _(−(OP4)) =V _(+(OP4))   (18)

Thus, when the first switch SW1 is turned on, the constant current mayflow through the capacitor C of the triangular wave generating sub-unit541. In this case, the constant current Ic is expressed as the followingequation 19:

$\begin{matrix}{I_{o} = \frac{V_{ref} - V_{B}}{R_{12}}} & (19)\end{matrix}$

According to the voltage-current relationship equation of the capacitorC, the output voltage Vout of the triangular wave generating sub-unit541 is expressed as the following equation 20:

$\begin{matrix}{V_{{out}{(A)}} = {{\frac{1}{C}{\int{I_{C}{t}}}} = {{\frac{1}{C}{\int{\frac{\left( {V_{ref} - V_{B}} \right)}{R_{12}}{t}}}} = {\frac{1}{C}\left( \frac{\left( {V_{ref} - V_{B}} \right)}{R_{12}} \right)}}}} & (20)\end{matrix}$

FIG. 21 is a circuit diagram showing a current balance control unit ofthe DC-DC converter including a triangular wave control unit accordingto the second embodiment.

Referring to FIG. 21, as the capacitor C of the first triangular wavegenerating sub-unit 541 is charged, the voltage Vout(A) is increased.The triangular wave control unit 420 reads out the increasing voltageVout and outputs the signal Ton having a low level when the voltage Voutreaches to the voltage value corresponding to the control current Ic, sothat the second switch SW2 is turned on by the signal Ton providedthrough the inverter 430. When the second switch SW2 is turned on, thecapacitor C is discharged. While the above-described operation isrepeated, the triangular wave may be output to the terminal Vout.

According to the above-described relationship equations, when thesensing current of an arbitrary block is increased so that the sensingcurrent is greater than the current average value of the sensingcurrents of all blocks, the value of the second output voltage Vo(A, B,C or D) is decreased, so that the gradient of the triangular wave of thetriangular wave generating unit corresponding to the above is increased.Thus, the turn-on time of the switch device SW of the DC-DC converter100 is decreased so that the current of the corresponding block isdecreased. As the above-described operation is repeated, the outputcurrents of all blocks are equal to each other. In addition, the secondembodiment can be operated in the current continuous mode as well as thecurrent discontinuous mode. That is, although the unstable operationscheme has been described, in which one block is operated in the currentcontinuous mode and other blocks are operated in the currentdiscontinuous mode when a DC-DC converter is operated in the currentcontinuous mode, according to the second embodiment, since the outputcurrent of the DC-DC converter 100 is fed back to the DC-DC converter100 such that the output currents may be balanced, all blocks areenabled to be operated in the current continuous mode.

In addition, the gradient of the triangular wave may be adjusted bysensing the currents of each block. In this case, it is possible toimplement the used sensing resistor having about 1 mOhm.

When the resistance value of the first resistor R1 which is the sensingresistor is reduced, the power loss reduced is expressed as thefollowing equation:

P _(loss) =I _(out) ² ×R ₁=62.5²×1×10⁻³=3.9 [W]

Even when the first resistor R1 which is a sensing resistor isimplemented to have a low resistance value, the sensing voltage isamplified by the first amplifier OP1 of the current sensing unit 510 andthen, is amplified by the second amplifier OP2 in the differentialamplification scheme once more while noise is removed. As describedabove, since the sensing voltage Vout is amplified through severalstages, even if the sensing voltage has a low value, the sensing voltagecan be sensed. Thus, the resistance value of the first resistor R1 islowered so that the power consumed in sensing can be reduced.

In addition, in the current mode control scheme, the consumed sensingpower is 62.5 W in the related art, but the consumed sensing power ofthe second embodiment is reduced to 3.9 W. Therefore, difficulty inselecting the sensing resistor corresponding to the high consuming powercan be overcome.

Meanwhile, the second embodiment may be applicable to a convertercapable of processing a high current and may be used for supplying powerto many electronic components required in a home appliance. In detail,the second embodiment may be used for a power supply of an energystorage system (ESS) for supplying power, an ESS for a renewable powergeneration farm, an ESS for transmission/distribution, an ESS for asolar/wind generation farm, etc.

Specifically, the second embodiment may be applicable to a low-powerbattery charging system requiring a current of 10 A or less, a fuelcell, or an electric vehicle having a battery pack.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A DC/DC converter comprising: n converters, eachconverter comprising a first switch device, connected in parallel toeach other and configured to adjust a level of an input voltageaccording to a duty ratio of a first pulse signal applied to the firstswitch device to output an output voltage, wherein the n is an integerof 2 or more; and a control unit configured to compare an average of nsensing currents with the n sensing currents sensed from the nconverters, respectively, to adjust the duty ratio of the first pulsesignal, wherein the control unit comprises: a current sensing unitconfigured to detect and amplify the n sensing currents to output nfirst output voltages; an average unit configured to average the n firstoutput voltages to output an average voltage; a current balance unitconfigured to compare the average voltage with the n first outputvoltages to output n second output voltages, wherein the duty ratio ofthe first pulse signal is adjusted by one of the n second outputvoltages.
 2. The DC/DC converter of claim 1, wherein the control unitfurther includes: a triangular wave generating unit configured togenerate n triangular waves having gradients adjusted according to eachof the n second output voltages.
 3. The DC/DC converter of claim 2,wherein the current sensing unit includes first to n-th current sensingsub-units, and each of the first to n-th current sensing sub-unitsdetects one of the n sensing currents and outputs one of the n firstoutput voltages.
 4. The DC/DC converter of claim 3, wherein the currentbalance unit includes first to n-th current balance sub-units, and eachof the first to n-th current balance sub-units compares the averagevoltage with one of the n first output voltages to output one of the nsecond output voltages.
 5. The DC/DC converter of claim 4, wherein thetriangular wave generating unit includes first to n-th triangular wavegenerating sub-units, and each of the first to n-th triangular wavegenerating sub-units outputs one of the n triangular waves which have agradient according to a level of one of the n second output voltages. 6.The DC/DC converter of claim 5, wherein the control unit furtherincludes: an error amplifier configured to compare each of the n outputvoltages of the n converters with a reference voltage and to amplifyerrors of the n output voltages to output the n control signals; and acomparator configured to compare one of the n control signals with oneof the n triangular waves to control one of first switches of each ofthe n converters.
 7. The DC/DC converter of claim 6, wherein the controlunit further includes n constant current sources configured to providemutually different currents according to each of the n second outputvoltages.
 8. The DC/DC converter of claim 7, wherein the triangular wavegenerating unit includes: n capacitors charged with each of n constantcurrents output from each of the n constant current sources; n secondswitch devices configured to control a charge or a discharge of each ofthe n capacitors; and a triangular wave control unit configured tocontrol the n second switch devices to be turned on or off.
 9. The DC/DCconverter of claim 8, wherein the triangular wave control unit controlsone of the n second switch devices based on one of charged voltages ofthe n capacitors and one of the n control signals.
 10. The DC/DCconverter of claim 9, wherein the triangular wave is a voltage betweenboth terminals of each of the n capacitor.
 11. A DC/DC convertercomprising: a plurality of converters connected in parallel to eachother and configured to adjust a level of an input voltage according toa duty ratio of a first pulse signal applied to a first switch device tooutput an output voltage; current sensing units configured to amplifysensing voltages by output currents of the converters flowing through asensing resistor in order to output first output voltages; and currentbalance units configured to amplify a differential signal between anaverage voltage of the first output voltages and one of the first outputvoltages in order to output second output voltages, wherein the dutyratio of the first pulse signal is controlled according to levels of thesecond output voltages.
 12. The DC/DC converter of claim 11, whereineach of the current sensing units includes: a first amplifier configuredto non-inverting amplify the sensing voltage; and a second amplifierconfigured to amplify a differential signal between an output of thefirst amplifier and the sensing signal.
 13. The DC/DC converter of claim11, wherein each of the current balance units includes a third amplifierconfigured to amplify a differential signal between an output voltage ofthe second amplifier and the average voltage.
 14. The DC/DC converter ofclaim 13, further comprising a constant current source configured tooutput a constant current based on an output voltage of the thirdamplifier.
 15. The DC/DC converter of claim 14, further comprising atriangular wave generating unit configured to generate a triangular waveby the current output from the constant current source.
 16. The DC/DCconverter of claim 15, wherein the duty ratio of the first pulse signalis controlled according to a gradient of the triangular wave output fromthe triangular wave generating unit.
 17. The DC/DC converter of claim15, wherein the triangular wave generating unit includes: a capacitorcharged with the current output from the constant current source; asecond switch device connected to the capacitor and configured toconnect the capacitor to a ground to discharge the capacitor; and atriangular wave control unit configured to control the second switchdevice.
 18. The DC/DC converter of claim 17, wherein the triangular wavecontrol unit is configured to turn on or off the second switch deviceaccording to the charged voltage of the capacitor.
 19. The DC/DCconverter of claim 12, further comprising an averaging unit configuredto generate the average voltage, and wherein the average unit includes abuffer configured to average the first output voltages to output theaverage voltage.
 20. A power supply of an energy storage systemincluding a DC-DC converter, in which the DC-DC converter comprises: nconverters connected in parallel to each other and configured to adjusta level of an input voltage according to a duty ratio of a first pulsesignal applied to a first switch device to output an output voltage,wherein the n is an integer of 2 or more; and a control unit configuredto compare an average of n sensing currents with the n sensing currents,respectively, to adjust the duty ratio of the first pulse signal,wherein the n sensing currents are sensed from each of the converters.21. A DC/DC converter comprising: at least one converter configured toadjust a level of input voltage according to a duty ratio of a firstpulse signal applied to a first switch device to output an outputvoltage; at least one control unit configured to control the on/offoperation of the first switch device to adjust the duty ratio of thefirst pulse signal.
 22. The DC/DC converter of claims 21, wherein aplurality of converters are connected in parallel, and each converter iscontrolled by a separate control unit.
 23. The DC/DC converter of claim21, wherein the control unit comprises: an error amplifier configured toamplify an error of the output voltage and to output an error current; atriangular wave generating unit configured to produce a triangular wave;a comparator configured to compare a peak value of the triangular wavewith the error current from the error amplifier and produce an outputsignal; and a latch unit configured to switch-on and switch-off thefirst switch device based on the output signal from the comparator. 24.The DC/DC converter of claims 23, wherein the triangular wave generatingunit comprises: a constant current source configured to produce aconstant current; a triangular wave control unit configured to output apulse signal; an inverter configured to invert the pulse signal receivedfrom the triangular control unit and output the inverted pulse signal; acapacitor configured to be charged by the constant current from theconstant current source; and a second switch device configured tocontrol charging and discharging of the capacitor based on the invertedpule signal so that the triangular wave generating unit outputs thetriangular wave to the comparator.
 25. A method for controlling a DC/DCconverter, the DC/DC converter comprised of a plurality of convertersconnected in parallel, comprising the steps of: adjusting a level of aninput voltage according to a duty ratio of a first pulse signal appliedto a first switch device to output an output voltage; and comparing anaverage of a plurality of sensing currents, wherein the plurality ofsensing currents are sensed from the plurality of converters,respectively, to adjust the duty ratio of the first pulse signal.
 26. Amethod for controlling a DC/DC converter, the DC/DC converter comprisedof a plurality of converters connected in parallel, comprising the stepsof: adjusting a level of an input voltage according to a duty ratio of afirst pulse signal applied to a first switch device to output an outputvoltage; amplifying sensing voltages by output currents of theconverters flowing through a sensing resistor in order to output firstoutput voltages; and amplifying a differential signal between an averagevoltage of the first output voltages and one of the first outputvoltages in order to output second output voltages, wherein the dutyratio of the first pulse signal is controlled according to levels of thesecond output voltages.